I have one betta too that prefers his one gallon (I've tried to put him in a 5 and a 20 and he hates it both times).
I have been guilt tripped too for things like that on other forums or even by fish store employees (never at Petsmart oddly enough) who just assume I'm an idiot if I have a question. Once, I went to a LFS and there was a betta with OBVIOUS swim bladder disease. He was like a bobber and struggling too. So, I brought him up to the counter and politley let the guy know that the fish had swim bladder disease. He rolls his eyes and says it's a bacterial infection. I said, "He can't even swim farther than bobbing on the surface. He has swim bladder infection." This guy spent the next ten minutes trying to sell me this sick betta and offered me the medication for a bacterial infection as I was obviously wrong. He then tried to tell me about how they have labyrinth organs... I said, "I'm a animal biology major in college. I know they have labyrinth organs... Really." I gave him to another employee and my friend (who has had cichlids her whole life and the same guy tried to give her a "lesson" too) and I left.
Just shows that people are insecure and are not willing to learn the art of animal keeping. This goes beyond fish keeping (As I have more than just fish and aquariums)... Animal caretakers are a community of lovers and care-givers, but we all have to learn sometime, somehow, and from somewhere/one. It REALLY ticks me off to be treated like a moron or like I haven't done my research. I ask questions because I care...
.... Okay.... Better... Sorry! I promise I'm agreeing! :)